1. Field of the Invention
The present invention relates to an actuator element for converting electric energy into mechanical energy (mechanical displacement, stress, vibration, or the like), such as a display, a relay, an actuator (an actuator of the type for generating flexural displacement, for use in a servo displacement device or the like), or the like, and for converting mechanical energy into electric energy, such as a sensor (a filter, an acceleration sensor, a shock sensor, or the like), a transformer, a microphone, a sound producing member (a speaker or the like), a vibrator, or an oscillator (for power or communication use), and a device incorporating such an actuator element.
2. Description of the Related Art
In recent years, there has been a demand in the optical and precision machining fields for displacement elements for adjusting optical path lengths and positions in the order of submicrons and detection elements for detecting a minute displacement as a change in an electric signal.
To meet such a demand, efforts are being made to develop actuators and sensors (hereinafter referred to as actuator elements) which utilize a displacement based on an inverse piezoelectric effect or an electrostrictive effect that occurs when an electric field is applied to a piezoelectric/electrostrictive material such as a ferroelectric material or the like, or a reverse phenomenon.
In the above fields, the development of actuator elements which are inexpensive, small in size, operate under low voltages, and have high-speed response is under way.
As shown in FIG. 17, a conventional actuator element 200 has a ceramic substrate 202 and piezoelectric/electrostrictive operation units 204 formed on the ceramic substrate 202.
The ceramic substrate 202 has cavities 206 providing thin-plate portions functioning as vibration plates 208. The piezoelectric/electrostrictive operation units 204 are formed on the vibration plates 208. Each of the piezoelectric/electrostrictive operation units 204 has a lower electrode 210 directly formed on the vibration plate 208, a piezoelectric/electrostrictive layer 212 formed on the lower electrode 210, and an upper electrode 214 formed on the piezoelectric/electrostrictive layer 212.
If the piezoelectric/electrostrictive layer 212 is made of a piezoelectric material, then when a voltage is applied between the upper electrode 214 and the lower electrode 210 such that the voltage has the same positive and negative values as a voltage applied to polarize the piezoelectric/electrostrictive layer 212, the piezoelectric/electrostrictive layer 212 is flexurally displaced toward the cavity 206 due to the lateral effect of an electric field induced strain (see, for example, Japanese laid-open patent publication No. 7-202284).
The above actuator element 200 employs the vibration plates 208. Though the vibration plates 208 are advantageous in that they can amplify the displacement of the piezoelectric/electrostrictive layer 212, since the cavities 206 need to be formed in the ceramic substrate 202, there are limitations on efforts to make the actuator element 200 lower in profile, lighter in weight, and lower in cost.